Some computers use multiple power supplies such as pulse width modulation (PWM) power supplies to provide power separately to various components. In general, a PWM power supply includes a PWM circuit and a power stage. The PWM circuit forms an internal oscillating signal, and uses the internal oscillating signal to generate a PWM signal. The PWM circuit then outputs the PWM signal to the power stage which provides a power supply output voltage based on the duty ratio of the PWM signal. Generally, increasing the duty ratio of the PWM signal increases the output voltage. Conversely, decreasing the duty ratio of the PWM signal decreases the output voltage.
When the internal oscillating signals of multiple PWM power supplies are left unsynchronized in a computer, signaling difficulties may occur. In particular, random electromagnetic interference (EMI) created by the PWM power supplies may influence the operation of the computer. In some situations, the interference (or noise) may be strong enough to corrupt particular signals or data causing the computer to operate incorrectly.
Synchronization of the PWM power supplies (e.g., synchronization of the internal oscillating signals) reduces the randomness of the EMI generated by the power supplies. Accordingly, such interference becomes more predictable, and the difficulties it causes can be dealt with in a controlled manner (e.g., using appropriate filters, or increasing particular signal tolerances).
One conventional approach to synchronizing PWM power supplies is to connect the PWM power supplies in a master/slave configuration. In such a configuration, the master power supply has the fastest oscillating signal, and each slave power supply has a slower oscillating signal. If there is no clear master power supply, the oscillating signal of one of the power supplies is purposefully made faster than the others. During operation, the master power supply uses a master power supply oscillating signal, and each slave power supply speeds up the frequency of its oscillating signal to match that of the master power supply.
Another conventional approach is to connect the PWM power supplies in a daisy chain (or loop) configuration such that each power supply drives the next. That is, the oscillating signal of each PWM power supply in the chain drives the oscillating signal of the next PWM power supply in the chain. In this configuration, there is no master power supply, and the oscillating signals tend to synchronize over time.